In service station environments, fuel is typically delivered to fuel dispensers from underground storage tanks (USTs), sometimes referred to as fuel storage tanks. USTs are large containers located beneath the ground that hold fuel. A separate UST is provided for each fuel type, such as low octane gasoline, high-octane gasoline, and diesel fuel. In order to deliver the fuel from the USTs to the fuel dispensers, a submersible turbine pump (STP) is typically provided that pumps the fuel out of the UST and delivers the fuel through a main fuel piping conduit that runs beneath the ground in the service station. Other types of pumps other than a STP, such as a self-contained pump within the dispenser housing for example, may be employed.
Due to environmental and possible regulatory requirements governing service stations, fuel-handling components that handle fuel or vapor and would leak the fuel or vapor to the environment if a leak existed may need to be secondarily contained. Examples of fuel-handling components include, but are not limited to fuel storage tanks, fuel piping conduits that carry fuel, STPs, main fuel piping, branch fuel piping, sumps, shear valves, and dispenser piping. Secondary containment is typically provided in the form of a sealed outer piping or outer container that surrounds the fuel-handling component whereby a space, called an “interstitial space” is formed between the fuel-handing component and the outer container or piping. If a leak occurs in the fuel-handling component, the leak is trapped in the interstitial space provided by the outer piping or outer container. Thus, the leak is prevented from leaking to the environment. The secondary containment must periodically be checked and evacuated.
It is possible that the secondary containment could also contain a leak unknown to service station operators. In this instance, if a leak were to occur in a fuel-handling component, the leak may escape to the environment through the leak in the secondary containment. For example, if the fuel-handling component is a double-walled fuel piping, wherein an outer piping surrounds and inner piping that carries fuel, and a leak exists in both the inner and outer piping, fuel from the inner piping may leak to the environment through the outer piping. Thus, without monitoring of the interstitial spaces provided by the secondary containment, it is possible that a leak can occur to the environment without being detected. The STP will continue to operate as normal, drawing fuel from the UST and providing fuel to the source of the leak.
Recent proposed changes in state and federal regulations will tighten the requirements to contain leaks via secondary containment and will further require better leak detection so that environmental damage may be minimized. As a result, it is becoming imperative that all potential leak sources be evaluated and steps taken to detect and contain leaks in the piping systems. If the interstitial space of the secondarily contained fuel-handling components can be monitored to detect a leak or breach in either the fuel-handling component or the outer containment, a breach can typically be detected before the leak could escape to the environment.
One method of monitoring the interstitial space of secondarily contained fuel-handling components for leaks is by drawing a vacuum level in the interstitial space. Examples of such systems are the aforementioned U.S. Pat. Nos. 6,834,534; 6,977,042; 6,978,661; and 7,010,961, U.S. Patent Application Publication Nos. 2004/0045343 A1; 2005/0039518 A1; 2005/0145015 A1; 2005/0145016 A1; and 2005/0247111 A1; and U.S. patent application Ser. No. 11/255,421, now U.S. Pat. No. 7,076,994. In these systems, a vacuum-generating source, which may be from a siphon port on the STP for example, draws a vacuum in the interstitial space. Thereafter, the interstitial space is monitored for pressure variations. If a sufficient pressure variation occurs, this is an indication that either the fuel-handling component or the outer containment has incurred a leak or breach due to the ingress or egress of fuel and/or air into the interstitial space either from the fuel-handling component or from the outside air.
When the secondarily contained fuel-handling component is piping or fuel line that carries fuel for example, the piping typically extends having one end close to the vacuum-generating source and a far end farthest away from the vacuum-generating source. As the vacuum-generating source generates a vacuum level in the interstitial space, the vacuum travels from the close end to the far end. However, if a blockage exists in the interstitial space between the ends, a vacuum level can still be maintained in the end of the fuel piping between the vacuum-generating source and the blockage even with the vacuum level extending on the far end side of the blockage. Thus, a monitoring system may still detect that a sufficient vacuum level is being maintained in the unblocked portion of the fuel piping. The blocked portion of the fuel piping may contain a leak, but it will go undetected due to the blockage.
Thus, an improvement of the aforementioned secondary containment monitoring and control system is to ensure that the vacuum level generated in the interstitial space reaches the entire length of the piping in order to ensure that a blockage does not exist and so that a leak anywhere along the piping is properly detected.